Many bicycles and other people powered vehicles are equipped with variable speed transmissions. The transmissions of these vehicles are shifted in order to permit changes in wheel torque and gear speed ratios so that the operator of the vehicle may pedal in pedal speed and pedal torque operating ranges which are comfortable for a human.
While there are many people who enjoy manually shifting such variable speed transmissions, there are others who do not understand their theory of operation and merely want to enjoy the pleasure of riding the vehicle and the exercise without being bothered with gear shifting decisions. These people may shift improperly thereby damaging the mechanism and causing a rough, uncomfortable ride.
Bicycles are typically provided with one of two types of multi-speed transmissions. Some have internally geared rear hubs which come in 2, 3 and 5 speed versions. These may be shifted at any time while pedalling is stopped. Other bicycles have multiple sprockets and derailleurs in which the bicycle chain is moved from one sprocket to another while pedalling of the bicycle continues.
Some prior patents have shown speed sensing devices for automatically shifting the three speed type of transmissions. Others show automatic shifting transmissions which utilize special transmissions designed by the particular inventor.
There is, however, a need for an improved automatic shifting mechanism which can be added to a conventional bicycle without requiring any modification of the existing, conventional, manual shift mechanisms and which provide increased efficiency and improved shifting characteristics.
Another object of the present invention is to provide an automatic transmission which has less mass than prior devices so that less weight is added to the vehicle.
Still another object of the present invention is to provide a speed sensor for an automatic transmission which is designed to better withstand the torque applied to its parts during rapid acceleration and deceleration.
Prior art patents are found in Class 74, subclass 3 and Class 280, subclass 238 and include U.S. Pat. Nos. 3,830,521, 3,969,948, 3,926,020 and other patents.